The present invention relates to an ink jet recording apparatus having recording heads which move in the direction of width of recording paper, and discharges ink droplets onto recording paper in accordance with print data for printing images, and more specifically relates to the ink jet recording apparatus capable of controlling a platen-gap to an optimum position for the cleaning operation and also relates to a head cleaning control method in the ink jet recording apparatus.
Since the graphic process has become to be executed relatively easily owing to the development of personal computers, a recording apparatus is now required, which is capable of outputting in high quality, e.g., hard copies of color images displayed on a display screen.
In order to meet such a need, the recording apparatus mounting ink jet recording heads is provided. This ink jet recording apparatus is used for various printing including color printing because in a print mode the noise is relatively small and also small dots can be produced in high density.
This type of ink jet recording apparatus has ink jet recording heads for receiving ink supply from an ink storage means and a paper-feed means for transferring recording paper relative to the recording heads. While the recording heads are moved according to a print signal, ink droplets are ejected onto recording paper to form dots so that the printing operation is executed.
Due to dealing with ink of liquid, a process is executed to forcibly absorb and discharge ink from the recording heads in order to prevent clogging caused by filling ink into the recording heads or volatilization of ink solvent. Further, with providing a drive signal irrelevant to print data, ink droplets are discharged from nozzle openings of the heads.
The forcible ink discharge process for solving the ink head blocking problem is generally called the cleaning operation. When resuming the printing operation after a long halt or when the user presses down a cleaning switch to solve clogging of the ink heads, the recording heads are sealed with a capping means to apply a negative pressure for discharging ink droplets. Then, the wiping operation by a blade member comprised of elastic plates such as rubber is followed.
The operation to discharge ink droplets by applying the drive signal to the recording heads is generally called the flushing operation. The flushing operation recovers uneven meniscus near the nozzle openings of the heads by wiping and the like during the cleaning operation and is executed by a certain cycle in order to prevent clogging of the nozzle opening which discharges only few ink droplets during the printing operation.
On the other hand, in case that the printing operation is performed by the recording heads onto recording paper, a platen-gap regulating means is provided for regulating a space between a platen (paper guide plate) and the recording heads in proportion to the thickness of recording paper, so that the most suitable space between the recording heads and the surface of recording paper can be maintained. In this platen-gap regulating means, the space between the recording heads and the platen is adjusted by slightly moving in the vertical direction on the carriage side, whereon the recording heads are generally mounted.
A typical convention platen-gap regulating apparatus for regulating a gap between a platen and a recording head in proportion to the thickness of a recording medium is, as shown in FIG. 12, adapted to change the distance from a platen face or a printing reference position to a recording head h by rotating a guide member g1 situated closer to the recording head h out of a pair of guide members g1, g2 for guiding a carriage c by the displacement quantity of an eccentric shaft.
Since the recording head h in a conventional printer is turned by an angle .DELTA..theta. equivalent to a gap regulating quantity .delta. centering on the other guide member g2 before and after the gap is adjusted, the parallelism between the recording medium s and the recording head h is spoiled by the angle .DELTA..theta.; this results in inconvenience in that the printing position is displaced to that degree in the direction of a line or otherwise an image is deformed lengthwise in the direction of the line. In the case of a printer for forming color images in particular, the trouble is that the tone and the like are affected by the aforementioned displacement or deformation.
As described above, during the recording head cleaning operation, processes such as discharging ink droplets by sealing the recording heads with a capping means, wiping ink layers adhered on a head nozzle plate with a cleaning member made of elastic plates, e.g., rubber are performed. However, said recording heads are moved in the vertical direction by a platen-gap regulating means in proportion to the thickness of recording paper. The position of the recording heads are not fixed.
Therefore, when the recording heads are sealed by the capping means, adherence between the heads and the cap is likely to be unstable. Consequently, technical problems occur, such as insufficient function of discharging ink droplets from the heads or increased load on a carriage.
Also other technical problems occur, for example, poor quality of wiping on the surface of the head nozzle plate as a result of a change in an extent of a contact (interference amount) between the heads and the cleaning member, or taint by indiscreetly scattering ink which is wiped by the repelling operation of the cleaning member.